Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$22.34	8.164%	$24.1638	$24.16	$24.15	$24.20
Purchase #2	$43.51	3.623%	$45.0864	$45.09	$45.10	$45.10
Purchase #3	$152.65	5.294%	$160.7313	$160.73	$160.75	$160.70
Purchase #4	$34.63	8.726%	$37.6518	$37.65	$37.65	$37.70
Purchase #5	$34.85	7.835%	$37.5805	$37.58	$37.60	$37.60
Purchase #6	$19.96	9.626%	$21.8813	$21.88	$21.90	$21.90
Purchase #7	$207.26	7.278%	$222.3444	$222.34	$222.35	$222.30
7 purchase totals =	$515.20		$549.4395	$549.43	$549.50	$549.50